The global data traffics increase explosively, and newly-emerging services represented by video and streaming media services develop rapidly, so that dynamic, high-bandwidth and high-quality requirement data services become the main body of network traffics and drive the network to evolve towards the packetization. On an aspect of a transport network, it can be seen that it is exactly the result of the development of network traffic datamation that the development is from a traditional Synchronous Digital Hierarchy (SDH) circuit switching network to a Multi-Service Transfer Platform based on the SDH (MSTP) with multi-service access functions and the gradual evolution is to a Packet Transport Network (PTN) nowadays. Fundamentally, the circuit switching network can only provide the rigid pipeline and coarse-grained switching and cannot effectively meet the requirements of dynamism and burstiness of the data services, but the flexible pipeline and statistical multiplexing feature of the packet switching network are naturally adapted to the data services. However, the current packet switching is basically processed based on the electronic layer, the cost and enemy consumption are high, and with the rapid growth of the traffics, the processing bottleneck of the current packet switching is increasingly prominent, which is difficult to adapt to the high-speed, flexible, low-cost and low-energy requirements of the future networks. The optical network has an advantage of low cost, low energy consumption and high speed and large capacity, but the traditional optical circuit switching networks (such as Wavelength Division Multiplexing (WDM) and an Optical Transport Network (OTN)) can only provide the large-grained grid pipeline, which is short of the flexibility of the circuit packet switching and cannot effectively bear the data services.
In the access network, the Gigabit-Capable Passive Optical Network (GPON) technology combines the advantages of the optical layer and the electronic layer to a certain extent. In a downlink direction, the GPON technology, by means of optical layer broadcast, distributes a downlink signal sent by an Optical Line Terminal (OLT) to each Optical Network Unit (GNU) via an optical divider, and meanwhile, a bandwidth map of an uplink frame is carried in a downlink frame header, to indicate the sending time and length of the uplink data of each ONU; in an uplink direction, each ONU sends the data according to an indication of the bandwidth map, and multiplexes the data to one wavelength path via an optical coupler and uploads the data to the OLT. Therefore, the GPON possesses the characteristics of high speed and large capacity and low cost of the optical layer on one hand, and implements the optical-layer statistical multiplexing of the multi-channel data in the uplink direction on the other hand, which improves the flexibility and the bandwidth utilization. The GPON normally uses the star/tree networking topology, and a working principle thereof is suitable to bearing the multipoint-to-single point converged traffics (the north-south traffics predominate), thus the successful application and large-scale deployment are achieved in the access network.
However, with respect to non-converged application scenarios, such as a metro area core network and a data center internal switching network, the east-west oriented traffics account for a large proportion and even occupy a leading position, thus the GPON technology is apparently unsuitable (the east-west oriented traffics need to be forwarded by the electronic layer of the OLT, and the capacity of the GPON is limited). The Optical Burst Transport Network (OBTN) adopts the all-optical switching technology based on the Optical Burst (OB), and possesses the ability of optical layer bandwidth on demand and fast scheduling between arbitrary network node pairs, which can realize the dynamic adaptation and good support to various traffic scenarios (such as north-south oriented burst traffics and east-west oriented burst traffics, etc.), enhance the resource utilization efficiency and network flexibility, maintain the advantages of high speed and large capacity and low cost of the optical layer in the meantime, and be applicable to various star/tree/ring network topologies. FIG. 1 is a schematic diagram of a 4-node OBTN unidirectional ring network, wherein, each node is configured with a pair of fast tunable burst mode transmitter and fast tunable burst mode receiver (which can be extended into more); two wavelengths serve as data channels in the entire network, one wavelength serves as a control channel, and a node A is a master node. The technical characteristics of the OBTN will be briefly described as follows:
(1) The most basic transmission unit in the data channel is the OB. A guard time existing between the OBs serves as an interval, one or a plurality of OBs form a data frame, initial positions of corresponding OB frames and OB slots of different wavelength channels need to be aligned. The data channel uses a burst optical receiver/transmitter, burst data are directly transmitted at the optical layer between source and sink node pairs and do not need to be forwarded at the electronic layer by an intermediate node. The source end is required to converge and encapsulate client-side data packets to the OBs to send.
(2) The control channel and the data channel are separated. The OBTN uses an independent wavelength channel to bear control information, including Operations Administration and Maintenance (OAM) information, a bandwidth report used for collecting a bandwidth request of each node and a bandwidth map indicating each node to send/receive data, and a control frame is sent in advance of a corresponding data frame. The control channel can use a common optical receiver/transmitter as the transceiving device, and electric field processing is performed in each node, to receive and update the corresponding control information. A time sequence relationship between the control frame and the data frame is as shown in FIG. 2.
(3) The all-optical switching based on the OB is implemented by using a fast tunable optical device. The OBTN node can fast adjust a transmitting/receiving wavelength of the nanosecond (ns) grade transmitter/receiver, to select corresponding wavelengths and OB timeslots for performing burst data transmitting/receiving according to the bandwidth map, so as to achieve the all-optical switching based on the OB.
(4) The traffic-aware real-time optical layer resource scheduling. The OBTN uses a centralized control mode, each slave node periodically reports a bandwidth request to the master node through the control frame, and the master node allocates the wavelengths and OB timeslots according to the current resource state and a bandwidth allocation policy, and an allocation result is wrote into a bandwidth map, and then is distributed to each slave node by the control frame, to realize the fast optical layer resource scheduling according to the traffic requirements.
However, since the burst data packet is directly transmitted at the optical layer between the source and sink node pairs without going through the electric processing, it is subject to the restriction of wavelength consistency and timeslot consistency. As shown in FIG. 1, one burst data packet sent from the node A to a node D is appointed by the bandwidth map at the node A to be added at the 3rd OB timeslot of the corresponding data frame of the wavelength λ 1; due to the optical-layer direct transmission and no wavelength convertor and optical buffering (the wavelength convertor is high-cost and seriously affects the signal quality; and the optical buffering technology is not broken through), and when it passes through a node B and a node C to drop at the node D, the burst data packet must also occupy the 3rd OB timeslot of the corresponding data frame of the wavelength λ 1, but the wavelength and timeslot position cannot be changed. Furthermore, since the allocation of wavelengths and timeslots is subject to the above multiple restrictions and the bandwidth resources are limited, if the allocation is improper, resource conflicts will be caused, which leads to a large number of packet losses and seriously reduces the network performance. The resource conflicts in the OBTN mainly include the following three kinds:
(1) Transmitter resource conflict. One source end transmitter can and only can send the burst data on one wavelength at arbitrary timeslot position. As shown in the figure, the node A sends an A→D burst data packet at the 3rd OB timeslot of the corresponding data frame of the wavelength λ 1; at this point, if there is also one service with the node A as a source node on the 3rd OB timeslot of the corresponding data frame of the wavelength λ 2 in the bandwidth map, the transmitter resource conflict is generated.
(2) Receiver resource conflict. One destination end receiver can and only can receive the burst data on one wavelength at arbitrary timeslot position. As shown in the figure, the node D receives an A→D burst data packet at the 3rd OB timeslot of the corresponding data frame of the wavelength λ 1; at this point, if there is also one service with the node D as a destination node on the 3rd OB timeslot of the corresponding data frame of the wavelength λ 2 in the bandwidth map, the receiver resource conflict is generated.
(3) Link resource conflict. An arbitrary timeslot of a corresponding data frame of an arbitrary wavelength can and only can be allocated once in the same link. As shown in the figure, a service A→D occupies the 3rd OB timeslot of the corresponding data frame of the wavelength λ 1; at this point, if there is also a service B→A which occupies the 3rd OB timeslot of the corresponding data frame of the wavelength λ 1 in the bandwidth map, then the link resource conflict will be generated in a link BC and a link CD.